Method and device for encasing sensors adapted to sense the position or the movements of a vehicle

ABSTRACT

A sensor element, such as an accelerometer, for sensing the position and/or the movements of a vehicle body is protected by a device comprising at least two protective casings. An inner casing encloses the sensor and protects the sensor against at least contamination. At least one outer casing encloses the inner casing and sensor and further protects the sensor against at least mechanical damage and shock. The at least one outer casing is a vehicle light casing, such as a headlight or tail light casing.

The present invention relates to sensors for sensing the position and/orthe movements of a vehicle or a vehicle body.

In the last ten years or so, use has been made of so-called activesuspension, which is a system radically improving the performance of thevehicle, especially its road-holding qualities, by altering theparameters controlling the movements of the vehicle suspension andrepresented by the stiffness of the suspension and the dampening effectproduced by the dampers to reduce the risk of oscillations occurring inthe suspension.

This suspension system has been rendered more sophisticated by theactive supply of energy therein, e.g. in order to incline the vehiclefor purposes of compensation in a "motorcycle-type fashion" in thebends. Similar ideas have been implemented for high-speed trains, wherethe carriage body is inclined inwards towards the center of a movementthrough a curve. Such inclination of the vehicle body substantiallyimproves the road performance as well as the riding comfort of thedriver and the passengers, manifesting itself not only as a potentialityof increased average cruising speed but also as a safer travellingfunction and improved braking properties of the vehicle.

From the theoretical, mathematical point of view, it has been held thatthe position of a vehicle is best determined with the aid of aninertial-navigation system with a so-called sky-hook, in which theposition of the car in space can be determined. However, since suchsystems are extremely expensive as well as complicated to build, effortshave instead been made to measure the total movements of the car body toget an idea of the various movements that may arise, such as rocking,rolling, and vertical displacement of the center of gravity. When usingthis system, it is of extreme importance that these movements bedetermined with the utmost accuracy.

To this end, use is made of accelerometers, which are arranged atdifferent points in the vehicle. In a simple acceleration system, theaccelerometer is disposed at the center of mass of the vehicle. In moreadvanced systems, on the other hand, the accelerometers are disposed asperipherally as possible in the vehicle to give maximal deflection whenthe car body moves in certain patterns. In this context, the maximalforces of acceleration are in the order of 2 g. In terms ofconstruction, it is not very difficult to build an accelerometer havinga maximal output signal as early as 2 g. However, the demands of the carindustry are much higher. Thus, they require that an accelerometershould be able to withstand a fall to a concrete floor from a height of1 m. Accelerations of about 5000 g have been measured on such impacts,and it is regarded as difficult to build accelerometers withstanding anoptional shock of 5000 g while maintaining their properties at ±2 g.Today's accelerometers are thus built with several protective casings,where the innermost casing encloses the accelerometer and its seals, andthe outermost casing is made of, e.g. hard rubber or some other yieldingmaterial giving a certain deceleration distance, should theaccelerometer be exposed to extreme shocks.

This problem is the more complicated as it is impossible to determine byvisual inspection or a simple measuring operation whether anaccelerometer has been damaged, e.g. during transport or when beingmounted.

Another problem encountered in prior-art constructions concerns thepositions of the accelerometers in the vehicle. Naturally,accelerometers can be arranged in, e.g. the luggage boot, but it is muchmore difficult to find a suitable place in the front of the vehicle. Theengine compartment is regarded as one of the most difficult places forelectrical equipment. This is so because one then has to take intoconsideration not only temperatures ranging up to 120° C., but also therisk of chemical damage, e.g. from degreasing agents, oil, or water. Inaddition, the environment is extremely exacting also because ofelectrical conditions, since high voltages of up to 20,000 V will bemingled with signalling voltages.

In the light of these facts, one has had to equip the sensors arrangedin different places in the vehicle with special protective electronicsas well as an extremely environment-resistant casing, to protect thesensors from chemicals, high temperatures, and moisture migrationthrough contacts.

The accelerometers manufactured for the car industry are often soencased that they are, in appearance and shape, suggestive of relays orspark plugs. The assembly personnel may therefore easily come to regardaccelerometers as being equally resistant as spark plugs or relays.

Thus, one may conclude that it is today possible to mount accelerometerswherever one wishes in the vehicle, but this involves extremely highrequirements on the environmental resistance of the accelerometers withregard to multi-layer casings as well as the resistance to chemicals andtemperature. In addition, the accelerometer has to be extremelyimpact-resistant and also so designed that it cannot be incorrectlymounted. If the accelerometer is incorrectly mounted, it will emitcompletely false output signals. All in all, special demands thus haveto be placed either on the design of the accelerometer or on the fitter.Both of these requirements have proven difficult to meet.

There is a general trend within the car industry towards looking forsolutions where the amount of cabling is reduced. In today's cars,cabling stands for one of the highest individual costs. It is thereforeof particular interest to find assembly systems minimizing the amount ofcabling. When new auxiliary systems, such as active suspension, areintroduced, the amount of cabling increases considerably.

The car industry has reacted to this by gathering the functions of, e.g.the steering column components or the door components, such as locks,rear view mirrors and window lifts, in a submodule containing amicroprocessor. This processor will in turn transmit and process thesignals from various peripheral units. These signals will then betransmitted on a common bus system to a central computer, where theinformation can be further processed and whence it is transmitted tovarious setting means.

An object of the present invention is to reduce or obviate the aboveproblems while enabling less expensive production of interfaces withregard to the remaining electronics.

Many of the above demands and requirements are met if the sensor or theacceleration transducer is provided with a weatherproof andimpact-resistant casing which cannot be incorrectly mounted and isdisposed at each corner of the car and which preferably may be used alsofor other functions. Despite all these features and requirements beingwell-known, the solution to the above problems has not been obvious tothe expert. If, as in the present invention, the requirements for theaccelerometer are combined with the requirements for other functions ofthe vehicle, these problems may be solved in a surprisingly simple way.

Thus, the invention is based on the fact that, in modern cars, theparking lights, the blinkers, the brake lights and the tail lights aremounted in a casing which in turn is arranged at one of the four cornersof the car. In some cases, this also goes for the main headlights. Theseindicators or information transducers are so constructed that it isimpossible to confuse them, either in respect of design or in respect ofmounting location and orientation. The indicators are designed so as tobe able to withstand an environment at the boundary surface between"outside the car" and "inside the car", which means that they areextremely moisture-resistant as well as resistant to various types ofchemical and mechanical strain. If an accelerometer is also arranged inthe same casing, as in the invention, it can be mounted at a marginalcost in a protected fashion during the very assembly of the indicatorsor information transducers in the factory. In this instance, the outercasing is composed of the outer casing of the indicator, while theelectric connections largely may run in parallel with the other electricconnections of the indicator.

Thus, the invention relates to a method for protecting a sensor, asdefined in appended claim 1. In this method for protecting a sensorelement, such as an accelerometer, adapted to sense the position and/orthe movements of a vehicle body, the sensor element is thus enclosed byat least two protective casings providing protection against,respectively, contamination and mechanical damage and shocks, saidprotective casings being designed as an inner casing which in turn isenclosed by an outer easing. The method according to the invention ischaracterized in that the outer protective casing is designed as atleast a portion of a cover for a lighting device or an informationtransducer.

Expressed in another way, the inventive method resides in enclosing thesensor element by a protective casing providing protection againstcontamination, mechanical damage and shocks. This aspect is distinguisedby the protective casing being designed as an inner casing which in turnis enclosed by an outer casing designed as at least a portion of a coverfor a lighting device or an information transducer for the vehicle.

The invention further concerns a device for protecting a sensor, asdefined in appended claim 2. In this device for protecting a sensorelement, such as an accelerometer, adapted to sense the position and/orthe movements of a vehicle body, the sensor element is thus enclosed byat least two protective casings which are designed as an inner casingprotecting the sensor element against contamination, and an outer casingprotecting the sensor element against mechanical damage and shocks. Thedevice of the invention is characterized in that the outer protectivecasing is designed as at least a portion of a cover for a lightingdevice or an information transducer.

Expressed in another way, the inventive device serving to protect thesensor element comprises at least two protective casings, of which atleast one provides protection against contamination, and at least oneprovides protection against mechanical damage and shocks. According tothe invention, this device is characterized in that one of theprotective casings is designed as at least a portion of a cover for alighting device or an information transducer to fellow road-users. Inthis instance, the sensor element can be disposed in a protective casingdesigned to provide protection against contamination and itself arrangedin a cover providing protection against mechanical damage and shocks andserving as a cover for a lighting device and/or information transducerof the vehicle. According to the invention, the sensor element and thelighting device and/or information transducer of the vehicle may beconnected to a common microprocessor or computer.

According to the invention, the cabling of the sensor may thus becombined with that of other components in the outer protective casing.In systems utilizing a signal-bus cable, a sensor encased according tothe inventive method or a sensor arranged in accordance with theinvention, can constitute a submodule where information is also derivedfrom the sensor element (the accelerometer). Naturally, theaccelerometer may also be designed so as to be easily mountable in thecasing of the indicator by means of special contacts. In that case, theaccelerometer would be as easy to replace as the lamps used in theindicator.

The invention will be described in more detail below with reference tothe accompanying drawing, in which

FIG. 1 illustrates a headlight in which is incorporated anaccelerometer, and

FIG. 2 illustrates an indicator unit containing brake lights, positionlights and an accelerometer according to the invention.

In the invention, an accelerometer 10 is disposed in an inner casing 11which provides protection against dust and mechanical damage and whichis mounted in the interior of a headlight casing 13 by fastening means12. In conventional manner, this headlight casing 13 is made of ayielding material, such as plastics material, and contains a reflector14 and a lamp unit 15. The entire arrangement is covered by a lamp glass16. With this construction, the degree of sealing is high. Theaccelerometer 10 and the lamp unit 15 have a cable bundle 17 connectedto the electric system of the vehicle.

FIG. 2 illustrates a tail-light unit 18 comprising a lamp glass 19 and aframe 23. Reflectors 20 for different types of lamps are provided in theframe. In accordance with the invention, a sensor 21 is further disposedin a protective casing which is impact-resistant as well as resistant toother types of mechanical damage. As in FIG. 1, the various lamps andalso the accelerometer are connected to the electric system of thevehicle by a cable bundle 22.

To further improve the impact- and shock-resistance, the fastening means12 may be yielding, or an additional protective casing, e.g. of cellularplastic or cellular rubber, can be used in the arrangement.

By mounting, in accordance with the invention, a comparativelyshock-sensitive sensor (may withstand a maximum of some 200 g) in anouter yielding casing, e.g. of plastics, one automatically obtains adeceleration distance by elastic deformation, should the entirearrangement (of FIGS. 1 and 2) be dropped on the floor. Onlyinsignificant deformations of the material are needed to reduce theg-forces by 10-50 times. With the invention, the g-force acting on thesensor element proper may be reduced from 5000 g to some 100 g.

Since the accelerometer is encased in an obviously fragile component inthe present invention, there is a greater probability that thearrangement will be carefully handled (the car industry does in fact notrequire that light bulbs and glass components should withstand anaccidental fall to the floor!).

According to the invention, the accelerometer or the sensor element isprovided with basic protection against dirt (optionally dust-proofprotection), a certain resistance to chemicals, as well as a basicability to withstand excessive load owing to its inner protectivecasing. As a rule, the latter is obtained from the manufacturer of theaccelerometer. By further providing, in accordance with the invention,the accelerometer or the sensor element with an outer protective casing,which also serves another purpose, i.e. to cover the lighting device orinformation transducer (e.g. the blinker or the brake lights), the outercasing will provide a deformation zone (elastic or plastic deformation),mechanical protection as well as chemical protection (against liquidsand gases). There is in addition a psychological factor by the fitterbecoming more careful when the component in which the sensor element ismounted appears to be fragile.

I claim:
 1. A method for protecting a vehicle motion sensor from contamination and shock comprising the steps of:enclosing the sensor with a first inner casing to produce an inner sensor assembly; and enclosing said inner sensor assembly with at least one outer casing; wherein said at least one outer casing comprises a vehicle light casing.
 2. The method of claim 1 wherein the step of enclosing said inner sensor assembly further comprises enclosing said inner sensor assembly with a headlight casing.
 3. The method of claim 1 wherein the step of enclosing said inner sensor assembly further comprises enclosing said inner sensor assembly with a tail light casing.
 4. A vehicle motion sensor protection apparatus, comprising:a vehicle motion sensor for sensing the position and/or movement of a vehicle; an inner casing surrounding the sensor for protecting the sensor against at least contamination; and at least one outer casing surrounding the sensor and inner casing for protecting the sensor against at least shock; wherein said at least one outer casing comprises a vehicle light casing.
 5. The vehicle motion sensor protection apparatus of claim 4 wherein said vehicle light casing comprises a headlight casing.
 6. The vehicle motion sensor protection apparatus of claim 4 wherein said vehicle light casing comprises a tail light casing.
 7. The vehicle motion sensor protection apparatus of claim 4 wherein said vehicle motion sensor comprises an accelerometer. 